The invention relates to a local communication system, in which a signal source is able to send signals to a destination device. As an example, the invention relates to a switch (the signal source) which is physically separated from an electrical appliance (the destination device), for example because the switch and the appliance are located at different location in a building. In another example, the signal source is a computer and the destination device is a printer placed apart from the computer.
Such signal sources produce destination unspecific signals, that is, if more than one appliance were connected to the source, a signal from the signal source would affect them all; for example, a switch would affect all lamps connected to it, and all printers connected to one computer printer port would print in response to character codes.
Conventionally, for selective source-destination device communication, a separate private connection between each pair of source-destination device would be needed.
To improve upon this situation, it is known to use a shareable serial bus as connection between sources and destination devices.
Over a serial bus, successive bits of data are transmitted in time serial succession. Hence a serial bus requires only few wires for transferring an arbitrary amount of information (one signal wire plus a ground may suffice) therefore, it does not need to be more complicated, at least as a physical connection, than a direct signal source-destination device connection. This makes a serial bus very suitable for use for example in control systems in buildings.
Via a serial bus, frames carrying messages composed of successive items of information can be transmitted from one station to another. When such frames comprise, in series with other information, a destination address that determines a destination device for which the frame is destined, the bus can be shared by more than one such destination device. The advantage of sharing is that only one connection is needed to connect all destination devices and signal sources, thus reducing the overall number of connections needed for signal passing. Furthermore, adding stations or changing the connection pattern does not require a change of connection wiring. In general, signal transfers can be performed without need to know the physical location of the signal source and destination device concerned.
It would be desirable to use the shareable bus for any possible apparatus. However, in this case it is a problem that many existing signal sources which produce destination unspecific signals cannot send signals only to a selected destination device via a shareable bus.